Volume compensated stereophonic phonograph



Filed Feb. l1, 1960 R. H. JANowsKY ETAL VOLUME COMPENSATED STEREOPHONICPHONOGRAPH 01m/mel E VVV' All!

Oct. 20, 1964 United States Patent (IT-)ii ice Bassist Patented Oct. 20,1964 3,153,702 VLUME COMPENSATED STEREPHNXC PHNGGRAPH Ralph H..lanowshy, Lockport, and John H. Riggs, Kenmore, NSY., assignors to TheWurlitzer Company,

Chicago, lll., a corporation of @hie Filed Feb. 11, 1960, Ser. No. 3,15%3 Claims. (Cl. 179-1) This invention relates to stereophonic soundsystems adapted to automatically play a sequence of stereophonicrecordings, such for example as stereophonic records. Stereophonicrecords are played automatically by coin controlled phonographs orjukeboxes and by automatic background music systems.

Such automatic sound systems are designed to operate unattended toreproduce a succession of recordings at a volumetric level which issufficiently high to assure enjoyment of the music by those for whom therecordings are played. Yet, it is also extremely desirable that theloudness level at which the recordings are reproduced be limitedsufliciently to avoid disturbance or irritation of people within theaudible range of the reproduction system.

The problem of maintaining the volumetric output level of an automaticphonograph within the optimum limits while the machine operatesunattended over long periods is complicated by the fact that diterentrecords are recorded to have different degrees of inherent loudness.Thus, a degree of ampliication which provides an optimum loudness in thereproduction of a record having a relatively low inherent loudness mayproduce excessive loudness in the acoustical reproduction of a recordinghaving a relatively high inherent loudness.

The matter of adapting an automatic phonograph, which plays monophonicrecords exclusively, to compensate automatically for different degreesof loudness of the records played has been accomplished satisfactorily.However, the problem of providing for automatic compensation fordifferent degrees of inherent loudness in stereophonic records presentsmany complicated problems in the designing of automatic stereophonicphonograph systems. These problems which are peculiar to stereophonicphonograph systems make the expedients used in monophonic systems tocompensate for difterent degrees of inherent loudness of monophonicrecords unsuitable for use in stereophonic phonograph systems.

One object of the invention is to provide, for reproducing stereophonicrecords, a new and improved stereophonic sound system which preservesthe mutual independence of two sound channels used in the system, andhence maximizes the stereophonic effectiveness of the reproduced sounds,while at the same time operating automatically to provide a highlyeffective control of the acoustical loudness of the system to compensatefor different degrees of loudness of the successive records played.

Another object is to provide an automatic stereophonic phonograph orsound system of the character recited in the preceding object whichresponds accurately and with great etiiciency to dilferences in theinherent loudness of recordings, to accurately compensate for thedifferences in the inherent loudness of the recordings to maintain anoptimum acoustical output level in the stereophonic reproduction of therecordings, while the the same time preserving the full stereophoniccharacter of the reproduced sound.

A further object is to provide, in an automatic phonograph, forattenuating the sound signals in an improved manner which isautomatically controlled to continuously compensate accurately for thedegree of inherent loudness of the successive records played by thephonograph.

Other objects and advantages will become apparent from the followingdescription, taken with reference to the single ligure of the drawing,which constitutes a diagrammatic illustration of a stereophonicphonograph forming the exemplary embodiment of the invention.

Referring to the drawing in greater detail, the automatic, stereophonicphonograph 10 forming the exemplary embodiment of the invention to bedescribed is illustrated diagrammatically in the single figure of thedrawing.

In the phonograph itl a succession of records 12 are automaticallypositioned on a turntable 14 and rotated in association with astereophonic pickup 16 which supplies independent electrical soundsignals through two separate outlets or terminals 18, 2t) of the pickup.

The electric sound signals supplied to the respective pickup outlets l,20 are separately amplified respectively in two electronic amplifyingchannels identified in the drawing by the legend Channel A and ChannelB, and operating to drive stereophonic loud-speakers 22, 2.4. Thus, thepickup output 18 is coupled through a capacitor 26 with a preamplifier23 in Channel A which is connected through a conventional tone control3i) with the Channel A amplifier 32, which drives the loud-speaker 22.Similarly, the pickup outlet 20 is coupled through a capacitor 34 with apreamplifier 36 in Channel B which is connected through a tone control38 with an amplifier 40, which drives the loud-speaker 24.

As previously intimated, stereophonic records, like monophonic records,have different degrees of inherent loudness. Automatic phonographs, suchas the phonograph 10 illustrated, normally operate unattended over longperiods of time. In order to maintain the loudness of the acousticalreproduction of the records Within optimum limits, it is desirable toprovide some compensation in the system for the inherent loudness of therecordings being played. The problem of accomplishing this desired endis complicated in stereophonic phonograph systems by a number offactors. These include the necessity for maintaining the operatingindependence of the two sound channels in order to preserve the inherentadvantages of stereophonic reproduction of recordings. The expedient ofproviding automatic volume compensation in each sound channel inaccordance with the strength of the signal being amplied in the channelis unsuitable, in that the stereophonic effectiveness of the soundreproduction would be greatly diminished, even though the means used toprovide automatic volume compensation in the two channels arestructurally and operationally independent of each other. Thus, in orderto realize the full advantages of stereophonic sound reproduction, it isnecessary that either of the channels be capable of producing relativelyloud acoustical sounds.` Thus, in a sense, a contrast in the loudness ofsounds generated by the two sound channels is an essentialcharacteristic of fully eifective stereophonic sound reproduction. T oprovide automatic volume compensation in each sound channel which isoperationally independent of automatic volume compensation in the otherchannel would result in an undesirable diminution in the differentialloudness of the acoustical outputs of the two channels relative to thedifferential strength or loudness of the electrical sound signalssupplied to the two channels.

Further complications arise in properly compensating for differentdegrees of inherent loudness in stereophonic recordings from the factthat a marked difference in the strength or loudness of the soundsignals in the two sound channels may persist for an appreciable periodof time, as in the playing of stereophonic recordings of someorchestrations.

The degree to which the acoustical reproduction of a stereophonicrecording is excessively loud is a function enea-,vea

of the loudness of the sound produced by the one of the two soundchannels which is receiving the stronger input signals from Itherecording. In accordance with the invention, a highly effectivecompensation for the inherent loudness of the record being played isprovided in a stereophonic phonograph or similar sound system in amanner which preserves the full stereophonic effectiveof the soundreproduction. This is achieved, as will presently appear, by providingvolumetric compensation in both channels which is continuouslycontrolled automatically, in accordance with the stronger of the twosignals in the respective channels and in a manner which preserves theoperational independence of the channels.

Thus, having reference to the drawing, it will be noted that the inputside of the coupling capacitor 26 in Channel A is grounded through tworesistors 42, 44 connected in series and serving as a voltage divider. Atap 46 to adjacent ends of the resistors 42, 44 is coupled through acapacitor 48 with a volume control amplifier 50 for Channel A.

Preferably, the control amplifier Si) comprises two transistors 52, 54connected in cascade between the input coupling capacitor 48 and anoutput coupling capacitor 56. A power voltage is applied to theamplifier 56B through a conductor 58 connected through a resistor 60with a power line 62.

The volume control amplifier 64 for Channel B is similar in constructionand in its operation to the volume control amplifier 50 for Channel A.The input of the volume control amplifier 64 is coupled through acapacitor 66 and a voltage divider formed by two resistors 63 and '70with the input side of the input capacitor 345 in Channel B. The circuitof the amplifier 64 includes two transistors 72 and 74 connected incascade between the input coupling condenser 66 and the output couplingcondenser 76. A power voltage is applied to the amplifier 64 by thepreviously mentioned conductor 58.

The outputs of the two voltage control amplifiers Si), 64 are connectedthrough two rectifiers 73, 3f) with the input side of a filter circuit82. As shown, the filter circuit 82 comprises a resistor 84 having itsinput and output ends coupled to ground through two capacitors 36, 88. Aresistor 90 is shunted across the capacitor 88.

The connection of the two rectifiers 78, 8f3 between the outputs of thetwo volume control circuits Sil, 64 avoids interference of thesecircuits with each other, while at the same time applying to the inputof the filter circuit 32 the electrical output of the one of theamplifiers Sii, 64 which is excited by the stronger of the signals fromthe two outputs 18, 20 of the pickup 1d. It may be noted in passingthat, if desired, a preamplifying stage can be provided between thepickup outlet 18 and the resistor 42 in Channel A, with a similarpreamplifying state being provided between the pickup outlet 2f) and theresistor 68 in Channel B.

The lter circuit 82 has an electrical integrating or averaging action inproviding an electrical output at its outlet end 92 which is a functionof the output of the more excited one of the control amplifiers 50, 64over a short interval of time. By way of example, a suitable filter 82is formed by a resistor 84 of 47 kilohms, grounding capacitors 86, 88 of100 microfarads each and a shunting resistor 9i? of 470 kilohms. Afilter 82 formed of components having the exemplary values just recitedprovides an electrical output which is a functional average of theelectrical input to the filter over a period of time that is short inrelation to the time required to play a recording but at the same timerather extensive in relation to the time typically required in music toplay a note of music. ln fact, the period over which the describedfilter 82 will average functionally the input to the filter issufiiciently long to extend over the playing of a number of successivemusical notes of normal duration.

The electrical output of the filter circuit 82 is used to controlautomatic volume compensation means provided in both Channel A andChannel B.

Thus, as illustrated in the drawing, improved signal attenuating means94 provided in Channel A comprises an attenuating resistor 96 connectedbetween the capacitor T26 and the preamplifier 28. The output side ofthe attenuating resistor 96 is connected to ground through a bleedresistor 98 and a discharging rectifier 10i). The effective admittanceof the rectifier lfl with respect to the signal strength at the outputend of the resistor 96 is controlled by the electrical output of thelter circuit 32, which is connected through a rectifier 102 to dischargethrough the attenuating or bleed rectifier 100. Thus, as shown, theoutput side of the rectifier 102 is connected to a tap M34 between thebleed resistor 9S and the discharge rectifier idf).

in operation, the filter circuit 82 applies an electrical bias to thedischarge rectifier Mit), thus tending to cause the rectifier itt@ toconduct.

Admittance of the bleed rectifier lil@ to the sound signal strength atthe output end of the resistor 96, and hence the extent to which thissound signal is bled off through the resistor 93, is controlled by thedegree to which the rectifier liifi is biased -to conduct direct currentby the filter circuit 82. Hence, increases in the output of the filtercircuit 82 effects proportional increases in the degree to which thesound signal strength is bled off through the resistor 98, with anaccompanying attenuation of the sound signals by the attenuatingresistor 96, to produce the desired volume control in Channel A, whichcompensates for the inherent loudness of the record being played.

The loudness of Channel B is controlled in a similar manner. rl`hus, asshown7 an attenuating resistor 106 is connected between the capacitor 34and the preamplifier 36. A bleed resistor 10S is connected from theoutput end of the resistor 166 to ground through a bleed or attenuatingrectifier 119. The output of the filter circuit 82 is connected througha rectifier 112 with the input side of the bleed rectifier il@ tocontrol the admittance of the latter to the sound signals, and hencecontrol the attenuation of the signals through the resistor 106, inaccordance with the output of the filter circuit 82, which operates in amanner described to provide the desired overall compensation for theinherent loudness of the record being played.

It will be understood that the invention is not necessarily limited tothe particular embodiment illustrated, but includes variants andalternatives within the spirit and scope of the invention as defined bythe claims.

The invention is claimed as follows:

1. In a stereophonic amplifier for playing program sources of differentinherent loudness and having two amplifying sound channels, thecombination comprising two volume control networks having connectionswith said respective sound channels to vary controllably the volume ofelectronic sound signals which are transmitted through said respectivechannels; each of said volume control networks including circuitry thatis responsive to a variable control voltage applied thereto to effect acontrolled modification of the loudness of the sound signals passingthrough the corresponding channel, which modification is substantiallyuniform in degree for all sound signals passing through the associatedchannel and which is a function of the control voltage applied to thevolume control network; a voltage integrating network having an inputside and an output side and including circuitry which responds to theapplication of a variable voltage to the input side of the integratingnetwork to produce an output voltage which is a function of the voltage,averaged over a period of time that is sufficiently long to encompassthe playing of a number of musical notes of normal duration, that isapplied to the input side of the integrating network; means includingtwo rectifiers connecting the input side of said voltage integratingnetwork to said respective sound channels ahead of the connections withthe sound channels of said respective control networks to maintain theindependence of said channels and at the same time apply to the inputside of said integrating network a voltage which is a function of theloudness of the louder of the two sound signals in said channels, andmeans including two rectitiers connecting the output side of saidintegrating network in controlling relation to said respective controlnetworks.

2. In a stereophonic music system, the combination of two separateparallel channels for electronic music signals, two volume controlnetworks having connections with said respective channels to varycontrollably the volume of electronic music signals which aretransmitted through said respective channels; each of said volumecontrol networks including circuitry that is responsive to a variablecontrol voltage applied thereto to effect a controlled modification ofthe loudness of the electronic music signals passing through thecorresponding channel, which modication is substantially uniform indegree for all sound signals passing through the corresponding channeland which is a function of the control voltage applied to the volumecontrol network; a voltage integrating network having an input side andan output side and including voltage integrating circuitry whichresponds to the application of a variable voltage to the input side ofthe integrating network to produce an output voltage which is a functionof the voltage applied to the input side of the integrating network andwhich output voltage is increased and decreased by said voltageintegrating circuitry only in response to increases and decreasesrespectively in the voltage applied to the input of the integratingnetwork and averaged over a period of time equal to the average timerequired to play a number of normal musical notes in succession, meansincluding two rectiliers connecting the input side of said integratingnetwork to said respective sound channels to maintain the independenceof said channels and at the same time apply to the input side of saidintegrating network a voltage which is a function of the loudness of thelouder of the two sound signals in said channels, and means connectingthe output side of said integrating network in controlling relation tosaid respective control networks, each of said last mentioned connectingmeans comprising a resistor connected -to the respective amplifyingchannel, a rectifier connecting said resistor to the output side of saidintegrating network, and a rectifier shunting to` ground the junction ofsaid resistor and said just-mentioned resistor, said last two rectiiersbeing similarly poled from the output side of said integrating networkto ground.

3. In a stereophonic amplier for playing program sources of differentinherent loudness and having two amplifying sound channels, thecombination comprising two volume control networks having connectionswith said respective channels to vary controllably the volume ofelectronic music signals which are transmitted through said respectivechannels, each of said volume control networks including circuitry thatis responsive to a variable control voltage applied thereto to effect asa function of the applied control voltage a controlled modication of theloudness of all the electronic music signals passing through thecorresponding channel; a voltage integrating network including a chokeresistor having an input side and an output side, a first ballastcapacitor connected between the input side of said choke resistor andground, and a second ballast capacitor and a bleed resistor connected inparallel between the output side of said choke resistor and ground; apair of rectifier means `connecting the input side of said chokeresistor to said respective sound channels to maintain the independenceof said channels and at the same time transmit -to the input side ofsaid choke resistor a voltage which is a function of the loudness of thelouder of the two sound signals in said channels, and means connectingthe output side of said choke resistor to Isaid respective controlnetworks to elfect control of said control networks in accordance withthe voltage on the output side of said choke resistor.

' References Cited in the iile of this patent UNITED STATES PATENTS2,249,606 Friebus July 15, 1941 2,336,880 Mitchell Dec. 14, 19432,536,664 Sinnett Ian. 2, 1951 2,703,825 MacDonald Mar. 8, 19552,714,633 Fine Aug. 2, 1955 2,799,735 Breckman et al July 16, 19573,077,519 Riggs et al Feb. 12, 1963

1. IN A STEREOPHONIC AMPLIFIER FOR PLAYING PROGRAM SOURCES OF DIFFERENTINHERENT LOUDNESS AND HAVING TWO AMPLIFYING SOUND CHANNELS, THECOMBINATION COMPRISING TWO VOLUME CONTROL NETWORKS HAVING CONNECTIONSWITH SAID RESPECTIVE SOUND CHANNELS TO VARY CONTROLLABLY THE VOLUME OFELECTRONIC SOUND SIGNALS WHICH ARE TRANSMITTED THROUGH SAID RESPECTIVECHANNELS; EACH OF SAID VOLUME CONTROL NETWORKS INCLUDING CIRCUITRY THATIS RESPONSIVE TO A VARIABLE CONTROL VOLTAGE APPLIED THERETO TO EFFECT ACONTROLLED MODIFICATION OF THE LOUDNESS OF THE SOUND SIGNALS PASSINGTHROUGH THE CORRESPONDING CHANNEL, WHICH MODIFICATION IS SUBSTANTIALLYUNIFORM IN DEGREE FOR ALL SOUND SIGNALS PASSING THROUGH THE ASSOCIATEDCHANNEL AND WHICH IS A FUNCTION OF THE CONTROL VOLTAGE APPLIED TO THEVOLUME CONTROL NETWORK; A VOLTAGE INTEGRATING NETWORK HAVING AN INPUTSIDE AND AN OUTPUT SIDE AND INCLUDING CIRCUITRY WHICH RESPONDS TO THEAPPLICATION OF A VARIABLE VOLTAGE TO THE INPUT SIDE OF THE INTEGRATINGNETWORK TO PRODUCE AN OUTPUT VOLTAGE WHICH IS A FUNCTION OF THE VOLTAGE,AVERAGED OVER A PERIOD OF TIME THAT IS SUFFICIENTLY LONG TO ENCOMPASSTHE PLAYING OF A NUMBER OF MUSICAL NOTES OF NORMAL DURATION, THAT ISAPPLIED TO THE INPUT SIDE OF THE INTEGRATING NETWORK; MEANS INCLUDINGTWO RECTIFIERS CONNECTING THE INPUT SIDE OF SAID VOLTAGE INTEGRATINGNETWORK TO SAID RESPECTIVE SOUND CHANNELS AHEAD OF THE CONNECTIONS WITHTHE SOUND CHANNELS OF SAID RESPECTIVE CONTROL NETWORKS TO MAINTAIN THEINDEPENDENCE OF SAID CHANNELS AND AT THE SAME TIME APPLY TO THE INPUTSIDE OF SAID INTEGRATING NETWORK A VOLTAGE WHICH IS A FUNCTION OF THELOUDNESS OF THE LOUDER OF THE TWO SOUND SIGNALS IN SAID CHANNELS, ANDMEANS INCLUDING TWO RECTIFIERS CONNECTING THE OUTPUT SIDE OF SAIDINTEGRATING NETWORK IN CONTROLLING RELATION TO SAID RESPECTIVE CONTROLNETWORKS.